1. Field of the Invention
This invention relates to valuable motor fuels which are characterized by high octane numbers, and reduced content of hydrocarbons, carbon monoxide and especially nitrogen oxides in the exhaust gases of an internal combustion engine using spark ignition. The fuels according to the invention attain octane numbers which make it possible to omit entirely any lead-containing additive.
The fuels of the invention are further characterized by a lower cloud point, increased oxidation stability and decreased specific energy consumption.
2. Description of the Prior Art
In order to increase the efficiency of the engine, which results in a lowering of the specific fuel consumption, the compression ratio is especially important. The resulting tendency of the engine to knock must be compensated by increasing the octane number of the fuel. For this purpose, anti-knock agents, particularly lead alkyls, alkylates or aromatics are added. Unfortunately, this causes an associated serious deterioration in the quality of the exhaust emissions. Besides poisonous combustion products of the lead compounds, an increase in the nitrogen oxide content is observed, due to high combustion chamber temperatures. If the lead content is decreased, the octane number can be adjusted by increased addition of aromatics. In place of a portion of the aromatics, octane-increasing isoparaffins, which are found in relatively large amounts in alkylate may be added.
However, a reduction in the pollutants, especially of nitrogen oxides, is not achieved by this expedient.
It is also known that the octane number can be increased and the exhaust gas pollution can be decreased by addition of methanol. However, in order to operate an internal combustion engine having spark ignition with a motor fuel containing more than 5% by volume of methanol, vehicles having such engines have to be equipped with methanol-resistant sealing materials. A further serious disadvantage of admixing more than 5% by volume of methanol is that in dual-fuel operation with a methanol-hydrocarbon mixture and a pure hydrocarbon mixture using conventional carburetors and injectors, the air-fuel ratio has to be adjusted so that the proportion of pollutants is kept within the exhaust limits for operation on pure hydrocarbons. An internal combustion engine with spark ignition which is adjusted to this fuel-air ratio can then no longer attain its maximum possible power output when operated on a methanol fuel containing more than 5% methanol by volume.
It is also known to add methyl tert-butyl ether or methyl tert-amyl ether to the fuel. It is a disadvantage that these constituents cannot be added by themselves in arbitrarily large proportions, since then DIN 51 600 and the other internationally prescribed standards of volatility for engine equipped with carburetors can no longer be met.